Field of the Invention
The present invention relates to an image forming apparatus, an image formation control program, and an image formation control method, and more particularly, to a technology for efficiently forming an image on a long paper sheet.
Description of the Related Art
An image forming apparatus normally forms images on paper sheets called cut paper sheets that are cut in a predetermined regular size such as “A4” or “B4”. However, an image forming apparatus can also form an image on a long paper sheet called a paper roll. A long paper sheet is used when a label is repeatedly printed, for example.
Control operation to be performed in an image forming apparatus that uses long paper sheets is disclosed in JP 6-278938 A, for example.
JP 6-278938 A discloses a printer for long paper sheets. The length of an A3 paper sheet as a cut paper sheet is 42 cm. Meanwhile, some long paper sheets are approximately 2.4 km long.
That is, a long paper sheet may be 5700 times longer than an A3 paper sheet. Therefore, as for a counter that manages paper sheet lengths, it is necessary to prepare a special counter that is capable of processing a large number of bits so as to cope with such a long paper sheet length. It is also necessary to provide an additional memory as an image memory. In short, so as to cope with long paper sheets, a conventional image forming apparatus that normally uses cut paper sheets needs to be greatly modified in terms of hardware and software.
In view of costs, however, a conventional image forming apparatus is expected to cope with long paper sheets, without any significant modifications made in its hardware and software.
FIG. 4 is a timing chart showing the control that is performed in a case where an image is repeatedly formed on a long paper sheet through the same control as that for an image forming apparatus using conventional cut paper sheets.
In this case, image data is repeatedly read out while various control signals are exchanged between the engine control unit in the image forming unit and the memory controller in the image storage unit. Time t passes in the direction from the top to the bottom of the chart.
In FIG. 4, (a) represents the engine control unit that controls the print engine in the image forming unit, (b) represents a top position signal VTOP indicating the position of the top edge of an image, (c) represents a valid region signal (VALID signal) indicating that an image can be formed in the conveyance direction (the sub scanning direction) of the paper sheet, (d) represents the memory controller that performs control to read out image data from the image memory in the image storage unit, and (e) represents image data read out from the image memory in the image storage unit.
Although the valid region signal might be a horizontal valid region signal (H-VALID) or a vertical valid region signal (V-VALID), a vertical valid region signal is described in this example. That is, the valid region signal (VALID) means a vertical valid region signal (V-VALID) in this example. Here, the vertical direction is the sheet conveyance direction, and the horizontal direction is a direction perpendicular to the sheet conveyance direction.
Referring now to the timing chart in FIG. 4, the control to be performed when an image is formed on a long paper sheet through the control for a conventional image forming apparatus designed for cut paper sheets is described.
At a start of image formation using a long paper sheet, the engine control unit transmits setting data related to image formation on a long paper sheet, to the memory controller ((01) in FIG. 4).
In this case, how many paper sheets of a regular size (such as A3 paper, which is the largest) are equivalent in length to the long paper sheet is calculated, and setting data generated so that the control for the paper sheets of the regular size will be repeated a predetermined times is transmitted. With this, a special counter for long paper sheets becomes unnecessary, for example.
Meanwhile, when preparation for image data readout from the image memory is completed, the memory controller transmits a preparation completion notification to the engine control unit ((02) in FIG. 4).
The engine control unit then raises the pulse of the top position signal indicating the position of the top edge of the image, in time with feeding of the long paper sheet from the sheet feeding unit ((1) in (b) in FIG. 4). The hatched portions of the pulse ((1) in (b) in FIG. 4) of the top position signal indicate that the top position signal is active. The engine control unit transmits the pulse ((1) in (b) in FIG. 4) of the top position signal to the memory controller ((2) in (b) in FIG. 4).
After receiving the pulse of the top position signal ((2) in (b) in FIG. 4), the memory controller raises the valid region signal in the sub scanning direction ((3) in (c) in FIG. 4) in accordance with the top position signal in an active state. In this case, the hatched portions of the valid region signal ((c) in FIG. 4) indicate that the valid region signal is active.
While this valid region signal ((c) in FIG. 4) is in an active state, the memory controller repeatedly reads image data from the image memory ((e) in FIG. 4). In this case, while the valid region signal is active, the memory controller reads image data twice at an interval t1.
The memory controller performs counting in the sub scanning direction of the paper sheets of the regular size. As a result of the counting, at the time equivalent to the bottom edge of a paper sheet of the regular size, the memory controller puts the valid region signal into an inactive state, and transmits a valid region signal termination notification to the engine control unit ((4) in (c) in FIG. 4).
After receiving the valid region signal termination notification, the engine control unit transmits a setting notification including next page setting data to the memory controller ((5) in FIG. 4).
When preparation for readout from the image memory is completed, the memory controller, which has received the setting notification including the next page setting data, transmits a preparation completion notification to the engine control unit ((6) in FIG. 4).
After receiving the preparation completion notification, the engine control unit raises the pulse of the top position signal indicating the position of the top edge of an image ((1) in the second and later tiers in (b) in FIG. 4), and repeatedly performs the same operation as above ((1), (2), (3), (4), (5), and (6) in the second and later tiers in FIG. 4).
After generating the top position signal a predetermined number of times, the engine control unit performs control not to generate the top position signal ((1′) and (2′) in (b) in FIG. 4).
Accordingly, the memory controller does not raise the valid region signal in the sub scanning direction ((3′) in (c) in FIG. 4), and stops reading out image data ((e) in FIG. 4).
In the above described control, the control operations of the respective components are involved in the transmission of a valid region signal termination signal from the memory controller to the engine control unit ((4) in FIG. 4), the transmission of a setting notification including next page setting data from the engine control unit to the memory controller ((5) in FIG. 4), and the transmission of a readout preparation operation and a preparation completion notification from the memory controller to the engine control unit ((6) in FIG. 4). Most of the control operations of the respective components are realized by software or the like. Therefore, a certain period of time is required, and the required period of time varies in some cases.
That is, time t2, which is the interval between image data readout operations and is the period of time during which the valid region signal is in an inactive state, cannot be fixed, and varies.
Further, time t1, which is the interval between image data readout operations and is the period of time during which the valid region signal is in an active state, can be fixed. However, since time t2 varies, time t1 and time t2 cannot be made uniform.
That is, when a label or the like is repeatedly printed on a long paper sheet with a conventional image forming apparatus designed for cut paper sheets without a special counter for long paper sheets, the intervals between printed portions such as labels cannot be made uniform, and productivity decreases by the amount equivalent to the interval unevenness, resulting in poorer efficiency.